Implantable medical devices are being used increasingly to monitor and assist functioning of the patient's organs. These types of devices includes cardiac stimulation devices e.g., pacemakers and ICDs, as well as insulin pumps and other mechanical devices. These devices are increasingly complicated thereby requiring increasingly complicated circuitry to be implanted in a casing within the body. Implanted devices are more convenient for the patient as an implanted device reduces the need for the patient to wear and accommodate an external device in their daily life.
Implantable devices, such as implantable cardiac stimulation devices, typically include a variety of electronic components such as batteries, sensing and stimulation circuits, microprocessors/controllers, and capacitors contained within a biocompatible enclosure. The enclosure is often made up of two clamshell halves which can be hingedly attached. The electrical components must generally be secured to a substrate such that the electrical components are secured to accommodate the movement of the implantable device when implanted within the patient. Consequently, when the casing is comprised of two clam shell halves, the electrical components are often secured to the interior surfaces of both of the clam shell halves. Both halves typically hold electrical components and the clamshell enclosures are typically positioned in an open configuration during manufacture or service of the device. Once the device is completed and ready for implantation, the clamshell halves are typically closed so as to be adjacent each other and essentially parallel. The clamshell halves form a hermetic seal in the closed position to exclude body fluids from the device electronics.
Many implantable medical devices, such as cardiac stimulation devices, are preferably as small as possible in order to minimize impact on the patient. The larger the casing, the more uncomfortable the implanted device is for the patient. The control, sensing, and stimulation circuitry, as well as the power supply, take up a considerable amount of room in the device enclosure. It is for these reasons that electrical components are typically installed in both halves of a clamshell enclosure. The electrical components in each clamshell half must typically be interconnected with electrical components in the opposing half. This imposes a requirement for an electrical interconnection that interconnects the various components in both halves with the enclosure in both the open and closed configuration.
Several methods are known in the art for interconnecting components in a plurality of relative positions. Slidable contacts, such as slip rings, are known to provide electrical contact throughout a range of sliding or rotational movement. However, slidable contacts are prone to corrosion at contact surfaces which can increase impedance and reduce signal transmission. In addition, slidable contacts, capable of conducting the relatively high voltage shocks that many implantable cardiac stimulation devices provide, tend to be large and occupy an undesirably large amount of the interior volume of the device.
Flat, straight ribbon cable is another known device for maintaining electrical contact between two electrical assemblies in relative motion. However, ribbon cable of known configurations is problematic with implantable medical devices as described above. In particular, the adjacent placement of the two clamshell halves in the closed position forces the ribbon cable into a tight bend such that the ribbon cable folds on itself. This places mechanical stress on the conductors and insulating material of the ribbon cable. This stress can compromise the electrical insulating ability of the insulation and lead to shorting and cross-talk between individual conductors of the cable. Further, sharp bends and other mechanical stresses can also result in the conductors breaking. In addition, the ribbon cable can only bend on itself to a limited radius and this bend or fold occupies an undesirably large interior volume in the device.
With most implantable medical devices and, in particular, implantable cardiac stimulation devices, the potential risks of conductors that are corroded or damaged as a result of the manner in which electrical components in each of the halves are interconnected is quite high. Electrical components may become disconnected potentially rendering the device inoperable. Consequently, many devices have made greater space allowances for electrical interconnect conductors which thereby either increases the size of the implantable medical device or decreases the available space for other necessary electrical components.
From the foregoing it will be appreciated that there is a continuing need in the implantable medical device field for an interconnection mechanism that reliably interconnects electrical components contained in opposing enclosure halves both in an open configuration and in a closed configuration as well as while moving between the two in a low profile fashion. The interconnection mechanism should not be under undue mechanical stress in either the open or closed configurations. There is a further need for an electrical interconnect that is durable and is not subject to the contact corrosion problems of slip-ring type contacts.